Cultured glomerular mesangial cells offer a means to study the contractile function of the glomerular mesangial cell in vitro. These cells, centrally located in the glomerulus, very likely play a key role in regulation of glomerular capillary blood flow and pressure. Exposure of the delicate network of glomerular capillaries to increased pressure and flows due to altered mesangial cell function may play a role in the pathogenesis of diabetic nephrosclerosis. Although direct comparisons of in vitro work with in vitro conditions is at best difficult, cell culture nevertheless provides a means to rapidly acquire information about the normal and abnormal con tractile properties of mesangial cells. It is anticipated that information gained from studies of cultured cells will provide important information about normal and abnormal cell function in diabetes which can be used as a starting point for appropriate in vivo studies. Thus, the long term goal is to increase understanding o the pathogenesis of diabetic nephrosclerosis. There are two specific aims for this proposal. One relates to characterization o an unknown vasopressin and insulin-responsive phospholipid molecule. Because vasopressin treatment of mesangial cells activates a sequence of receptor-mediate biochemical events leading to contraction, participation of this unknown phospholipid in these vasopressin-associated events is of potential importance in regulation of mesangial cell contraction. Further, the work of others and preliminary data from my laboratory suggest that insulin may cause turnover of this unidentified lipid. Because of its potential biological significance in relation to contraction and insulin action, we propose to characterize this molecule and being studies of its possible functional significance in mesangial cells. specific aim relates to continued studies of phosphoinositide metabolism. Experiments are proposed to address the significance of phosphoinositide metabolism as it relates to short and long term regulation of contraction function.